1. Field
The present invention generally relates to the field of position sensing and, more particularly, to the field of linear position transducers.
2. Background
Linear position transducers are used in a wide array of position measurement applications including, for example, industrial machines such as injection molding machines, robotic arms, and hydraulic actuators. Generally, linear position transducers can be divided into two categories: (1) stationary read head with moving scale; and (2) moving read head with stationary scale. In the stationary read head category, the read head is typically mounted on a machine frame while the scale is mounted on a moving table. Optical position transducer designs can be configured in this manner, where optical scanning and processor devices are mounted on the machine frame and a scale is mounted on the moving table. In this configuration, as the table moves in relation to the machine frame, the optical scanning device measures the linear position of the table. Current optical position transducer designs can measure linear position down to fractions of a micron.
Other linear position measurement applications require transducers in the moving read head category. In this category, the read head is mounted on a moving table or attached to a moving arm and the scale is mounted on a machine frame. Hydraulic cylinder designs can be configured in this manner, where the read head moves along a rod, in response to a change in pressure of a gas or fluid in a cylinder, and the scale is mounted on a stationary machine frame. In this configuration, conventional hydraulic cylinder designs require a cable attached to the read head to provide power and to obtain an accurate readout of position. For applications requiring a rapidly-moving read head or where cabling introduces undesirable constraint on the read head movement, such conventional designs do not provide a reliable solution.
One commonly used solution for applications requiring a moving read head along a stationary scale is the magnetostrictive sensor. In a magnetostrictive sensor, the position of a magnet moved along a rod can be sensed by sending an interrogation pulse down the rod. Such magnetostrictive sensors are useful for sensors placed in such challenging environments as the interior of hydraulic cylinders. However, their accuracy is limited to about 100 microns per meter.
What is needed is a linear position transducer that can reliably and wirelessly track rapid motion along a scale and provide greater accuracy than conventional sensors, such as the magnetostrictive sensor.